Telephone transmitter



July 3l, 1951 w. A. conn L 2,562,526

TELEPHONE TRANSMITTER Filed Dec. l, 1949 ffff 'l 1 ...if

INVENTOR. WILLIAM ALFRED CODD JKM v ATTORNEY Patented July 31, 1951 TELEPHONE TRANSIWITTER William Alfred Codd, Rochester, N. Y., assignor to Stromberg-Carlson Company, a corporation of New York Application December 1, 1949, Serial No. 130,501

Claims. l

This invention relates to improvements in sound translating apparatus and particularly to microphones of the class known as telephone transmitters.

Microphones of this class generally comprise a vibratile diaphragm adapted to compress comminuted resistance material in accordance with the sound waves striking the diaphragm. In such microphones, the comminuted resistance material usually is composed of carbon granules. The granules are contained within a chamber having two spaced apart electrodes. One electrode is stationary, and the other is arranged to be driven, o r vibrated, by the diaphragm. A source of direct current potential is connected between these electrodes, causing a current to now through the resistance material.V Under these conditions, actuation of the diaphragm by a sound Wave will cause a variation in the amount of current flowing through the resistance material. This action is termed modulationof the current.

In microphones known before my invention,

either the modulation efficiency and the resistance changed over Wide limits when the orientation, or position in space, of the microphone was changed, or else the modulation elciency was low. Resistance changes were generally the consequence of changes inapressure of the granules against the electrodes as the microphone was moved. In particular, the pressure increased when the microphone axis was horizontal, but decreased when the axis was vertical. y

Poor eficiency resulted from some microphone It is another object of my invention to provide.

a microphone having a modulation eliciency greater than that achieved by previously known microphones through the elimination of extrane-` ous granular masses and inefliciently modulated current paths.

-It is a stm further object of my invention to provide a microphone having an improved frequency response and a low degree of amplitude distortion.

In generaLI achieve theseand other objects of my invention by providing anew configuration for the microphone elements. As part of this coniiguration, I employ a pair of Substantially The extraneous masses -furthermore conically shaped electrodes, one stationary and the other movable. supported by the frame of the microphone, while the movable electrode is arranged to be driven by the diaphragm. These electrodes are arranged If free carbon granules are piled up on a horizontal surface, it will be found that the granules form a cone-shaped'heap. It will befound fur-V ther that the angle of the conical surface with.y

respect to the vertical axis of the conical heap is largely independent of the size of the heap; that is, the cone retains the same shape (though not.;

the same size) as more'granules are added. In

accordance with my invention, I prefer to employ electrodes having conical surfaces whose acute angle with respect to their axes is smaller than, the corresponding natural angle that would be asa. sumed by the granules when heaped in an uncon-` ned pile on a horizontal surface. `This insures that the granules within the main chamber will, not fall away from the electrode surfaces when` the microphone is oriented with the electrode axis vertical.

It is a feature of my invention that the majorf mass of carbon granules is confined to the spacev directly between the electrodes. In the illustrated embodiment of my invention, I accomplishr this confinement with a compressible means, suchv as a bellows. A main chamber is thus formed, having the electrodes as its ends and the compressible means as its side walls.

A further part in achieving the objects of my invention is played by a lling chamber located behind the stationary electrode, that is, on the side of the stationary electrode farthest from the main chamber. cates with the main chamber by meansfof one or more lling holes, preferably adjacent to the Both,

outer circumference of the main chamber. the lling and main chambers are substantially lled with granules.

chamber against the stationary electrode.

Another feature of my invention resides in a,

housing meeting themovable electrode at the smaller end of its frustum, extending away from' the stationary electrode, and closed at its end farthest from the main chamber. The housing,

The Stationary electrode isv I prefer the The filling chamber communie.

When the microphone is` oriented with the stationary electrode uppermost,A the pressure of the granules in the lling chamber increases the pressure of the granules in the main` like the main chamber, is substantially filled with granules andthusprovides a reservoir of granules. Although the housing may be attached to the movable electrode by any convenient means, I prefer that the housing be formed as an integral part of the movable electrode as by stamping or drawing the electrode material. When the movable electrode is uppermost, the. granulesin the housing are higher than those in the main chamber. The granules in the housing therefore increase the pressure of the granules in the main chamber against the concave-side of the movable electrode.

Still other objects andf'advantages of my invention will become apparent as the, following description; proceeds and the features of novelty- Whichcharacterize my invention will be pointed out with particularity in the claims annexed to and'forming a part'of this specication.

For a better understanding of my invention, reference may be had to the accompanying drawing in which Fig. 1` is a top view of a. preferred'embodment of my invention; and

Fl'g, 2 is a sectional view taken along line 2--2 in Fig. 11

Referring now' to the drawing, the microphone illustrated in Figs. 1 and 2 comprises an annular frame I made of a suitable substance, as for example metal. Supported by this frame is a vibratile diaphragm 2 which is clamped to frame I by some means such as the annular spacing ring.

3. Itis desirable to mount a dust and moisture shield 4A in front ofthe diaphragm 2. Frame I, diaphragml, spacing1 ring, 3, and shield 4, may be secured'in place by clamp 5, which crimps these parts together at their outermost circumference. To' allow sound wavesto passlthrough clamp 5, holes 6 are provided'therein.

Attached to the center of the diaphragmof the illustrated embodiment by some convenient means, such as spot-welding, is4 a movable elec.- trode' 'IofLfrusto-conical shape. having at its center portion a housing definedby a cylindrical por, tion.8, which is terminatedA at its outerV endby a portion 9. I prefer portions to be of hemispherical shape for ease of forming, but it may be. of any convenient shape thatwillattainmy aim of providinga reservoir. ofcarbon granules Aabovethe movable electrode 'I when the movable electrode is, above the stationary electrode I0.V This sta.- tlonary electrode Il! is. opposite electrode T, and is` of substantiallyconical shape. Furthermore, it isarrangedsuch that its., apex. extends in the vdirectionY of the first-mentioned electrode 7. As previously explained, the acute` angle of each electrode surface with respect to its axis is preferably no larger thanthe corresponding natural angle-'that would be assumed lby the4 granules when heaped'in an unconfinedpile on ahorizontal surface.

Electrode IIJV is provided. with llingl holes II which may be arrangedl ina circle coaxial with the conicallsectiom preferably adjacent to the outencircumference of the, main chamber. Electrodes Tand VIll'define the ends of `a main chamber substantially lled with carbongranules` I2. This chamber isof substantially cylindrical shape as determinedby compressible means I3. I prefer means I3. to be highly flexible in thev axial direction butnot in thek radial direction. Means I3` maybe aY bellows arrangement formed of asuitable material, such as paper, for` example. The folds ofbellows I3 are preferably madev closer together than the smallest of the carbon particles,

4 thus insuring that the resistance material will be confinedin the space directly between electrodes "I and I0.

It is convenient to form diaphragm 2 of metal,

, infwhich case electrode 'I is conductively connected to frame I. Frame I thus forms one terminalof'the'microphone. Frame I is insulated from electrode I0 by means of the annular insulating ring I #which extends between a shoulder I5on the-outerA circumference of electrode IU and a shoulder I6 on the inner circumference of frame I. Awashereshaped insulating disk I1 seals the microphone against the entry of air or moisture, and also serves t0 insulate electrode I0 from the clamping ring I8 used to clamp electrode I0 in fixedrelationship to frame I.

In assembling this embodiment of my invention, the microphone is rheld upside down from the position shown in the accompanying Fig. 2. Carbon granules are poured into filling chamber I9 and pass through lling holes I I, thus filling the housing (portions Sand 9) and the main chamber between electrodes 'I and I0 substantially completely. Filling space I9 is then lled with granules, and plug 20 is screwed into electrode I0 by means of threaded means 2 I.

In the preferred embodiment of my'invention', I provide a housing which meets thecentral portion of the frusto-conically shaped electrode 'I and extends away from the stationaryv electrodes. Although I have shown this housing being formed of a cylindrical portion 8` terminated by a hemispherical portion 9, it may be of any Shapesuit able for attaining maximum capacity in the housing with minimum cross-sectional area'.

When the microphone is oriented with electrode 'I uppermost, as shown in Fig, 2, the carbon granules within the housing exert pressure through the granular mass, thus increasing the pressure of the granules in the main chamber against the concave side of electrode 1. On the other hand, when the lmicrophone is inverted from the position shown in Fig. 2, the granules within the lling chamber I9 increase the pressure of the granules in the main chamber against the convex side of electrode I0. Thus the pressurev sistance of a carbon microphone (of given elec-- trode dimensions and spacing) depends to a considerable extent upon the pressure of the granules against the electrodes, it is seen that the tendency of the resistance to decrease when the microphone axis is vertical is largely counteracted.

The use of a compressible means, such as bellows I3, confines the granules to the space. between electrodes 'l and I 0, yet has suflicient ilexibility to allowfree vibration of electrode 1 with diaphragm 2. Because of this confinement, there are no extraneous granular masses present, as in some microphones; because there are'no extraneous granular masses present, the sound energy driving the diaphragm is effective to compress only granules between the electrodes. These granules are therefore fully modulated'1 and'the modulating eiciency is consequently improved over that of previously'known microphones intended to achieve minimum positionalvariation.

The elimination of extraneous granular massesY improves the frequency response of the microphone because in this way the diaphragm is as. It also results in` trede space is also benecial because the pressure increase when the microphone axis is horizontal is less than in previous microphones having extraneous granular masses. As previously pointed out, the pressure decrease when the axis is vertical is less, according to my invention, than in previously known microphones because of the housing defined by portions 8 and 9 and of lling chamber I9. In this way, the over-all range of pressure variation and consequently of resistance variation, is less than achieved before.

While I have shown and described a particular embodiment of my invention, other modifications will readily occur to those skilled in the art. For example, it is not necessary that the particular configuration of the housing dened by portions 8 and 9 be employed to produce beneficial results. Furthermore, other compressible means may be employed instead of bellows I3. I do not therefore desire my invention to be limited to the specic arrangement shown and described and I intend, in the appended claims, to cover all modifications within the spirit and scope of my invention.

What I claim is:

1. In a microphone, a vibratile diaphragm, two electrodes, one of said electrodes being stationary and having a convex surface and the other being movable with said diaphragm and having a concave surface, said two surfaces being generally cone shaped, being coaxial with each other and with said diaphragm and facing each other in mutually spaced relation to define the ends of a chamber; closure means yieldable only in a direction substantially parallel to the axis of said electrode surfaces and extending generally cylindrically around said chamber to completely dene said chamber; and comminuted resistance material completely filling said chamber and adapted to be compressed in accordance with incident sound waves; each of said electrodes having the acute angles between their respective generally cone shaped surfaces and their common axis smaller than the corresponding natural angle that would be assumed by said comminuted resistance material when heaped in an unconned pile on a horizontal surface; and said closure means including a bellows the folds of which extend inwardly to the cylindrical zone connecting the base portions of said cones in an axial direction and are so narrowly spaced as to substantially prevent said comminuted resistance material from entering said folds, thereby confining said material within the space between said electrodes.

2. In a microphone, a vibratile diaphragm, two electrodes, one of said electrodes being stationary and having a convex surface and the other being movable with said diaphragm and having a concave surface, said two surfaces being generally cone shaped, being coaxial with each other and with said diaphragm and facing each other in mutually spaced relation to dene the ends of a chamber; closure means yieldable only in a direction substantially parallel to the axis of said electrode surfaces and extending generally cylindrically around said chamber to completely define said chamber; and comminuted resistance material completely lling said chamber and adapted to be compressed in accordance with incident sound waves; and a filling chamber which is also filled with said material and is in communication with said rst mentioned chamber; each of said'electrodes having the acute angles between their respective generally cone shaped surfaces and their common axis smaller than the corresponding natural angle that would be assumed by said comminuted resistance material when heaped in an unconned pile on a horizontal surface; and said closure means including a bellows the folds of which extend inwardly to the cylindrical zone connecting the base portions of said cones in an axial direction and are so narrowly spaced as to substantially prevent said comminuted resistance material from entering said folds thereby confining said material within the space between said electrodes.

3. In a microphone, a vibratile diaphragm, two electrodes, one of said electrodes being stationary and having a convex surface which is generally cone shaped and the other of said electrodes being movable with said diaphragm and having a concave surface which is generally truncated-cone shaped, said two surfaces being coaxial with each other and with said diaphragm and facing each other in mutually spaced relation to define the ends of a chamber; yieldable closure means extending between and contiguously to the peripheral base portions of the cone formed by said surface of the stationary electrode and the truncated cone formed by said surface of the movable electrode, generally cylindrically around said chamber to completely define said chamber; comminuted resistance material completely filling said chamber and adapted to be compressed in accordance with incident sound waves; and a reservoir housing which is movable with said movable electrode, extends centrally from the smaller end of said truncated cone away from said chamber, is closed at the end farthest from said chamber, is also lled with said material and is in communication with said chamber; each of said electrodes having the acute angles between their respective generally cone shaped surfaces.

and their common axis smaller than the corresponding natural angle that would be assumed by said comminuted resistance material when heaped in an unconned pile on a horizontal surface; and said closure means being yieldable only in a direction substantially parallel to the axis of said electrode surfaces for confining said material within the space between said electrodes.

4. In a microphone, a vibratile diaphragm, two

electrodes, one of said electrodes being stationary and having a convex surface which is generally cone shaped and the other of said electrodes being movable with said diaphragm and having a concave surface which is generally truncated-cone shaped, said two surfaces being coaxial with each other and with said diaphragm and facing each other in mutually spaced relation to dene the ends of a chamber; yieldable closure means extending between and contiguously to the peripheral base portions of the cone formed by said surface of the stationary electrode and the truncated cone formed by said surface of the movable electrode, generally cylindrically around said chamb-er to completely define said chamber; comminuted resistance material completely filling said chamber and adapted to be compressed in accordance with incident sound waves; and a reservoir housing which is formed on said movable electrode, has a cylindrical portion extending centrally from the smaller end of said truncated cone away from said chamber, has a substantially hemispherical portion closing said housing at its chamber; each of said electrodes having the acute assegna angles between their respective: generally conev shaped surfaces and: their common axis smaller than Athe corresponding natural angle that;would be assumedbysaid comminuted resistance materialwhen heapediinzaniunconined pileion a horizontal; surface; and said` closure means being yieldable'only in a: direction substantially parallel to' the axis of saidelectrode surfaces for coniining said material within the space between said electrodes.

5. In4 a'microphone; alvibratile diaphragm, two electrodes, one of Asaid-'electiodes-being stationary and having a convex surface which is generally cone shaped and the other of said electrodes being movable with said diaphragm and having a concave surface which is generally truncated-cone shaped, said two surfaces being coaxial with each other and with said. diaphragm and facing each other in mutually spaced relation tol denne the ends of a chamber; yieldable closure means extending between and contiguously to the peripheral base portions of the cone formed by said surface of the stationary electrode and the truncated cone formed by said surface of the movable electrode, generally cylindrically around said chamber to completely define said chamber; comminuted resistance material completely fillingsaid chamber and adapted to be compressed in accordance with incident sound waves; a first reservoir housing which is located on the side of said stai.'

tionary electrode away from said chamber; and a second reservoir housing which is movable with said electrode, extends centrally from the smaller end of said truncated cone away from said chamber, and is closed at the-end farthest from said chamber; each of said electrodes having the acute angles between their respective generally cone shaped surfaces and their common axis smaller than the corresponding natural angle that would be assumed by said comminuted resistance material when heaped in an unconned pile on a horizontal surface; said closure means being yield-l able only in a direction substantially parallel to the axis of said electrode Surfaces for confining saidmaterial within the space between said electrodes; and both said reservoirs being also lled with said material and being in communication with saidchamber; whereby the range of pressure Variation of said material in said chamber is restricted. and the modulation efficiency of said microphone is maintained at a high level regardless of its orientation.

6. In a microphone, a vibratile diaphragm, two electrodes, one of said electrodes being stationary and having a convex surface which is generally cone shaped and the other of said electrodes being movable with said diaphragm and having a concave surface which is generally truncatedcone shaped, said twov surfaces being coaxial with each other and with said diaphragm and facing each other in mutually spaced relation to denne the ends of a chamber; yieldable closure means extending between and contiguously to the peripheral baseportions of the cone formed by said surface of the stationary electrode and the truncated cone formed by said surface of the movable electrode, generally cylindrically around said chamberto completely define said chamber; comminuted resistance material completely filling said chamber and adapted to be compressed in accordance with incident sound waves; a first reservoir housing which is located on the side of said stationary electrode away from said chamber; and a second reservoir housing which is formed on saidmovable electrode, has a cylindrical portion extendingcentrally` from the smaller end of said truncated cone away from said cham ber and a substantially' hemispherical portion closing said housing. at itsrend farthest from said chamber; each of saidelectrodes having the acute angles between their respective generally cone shaped surfaces and their common axis smallerv than the corresponding natural angle that would be assumed by said comminutedresistance material when heaped in an unconned pile on a horizontalsurface; said. closure means being yieldable only in' ar directionsubstantially parallel to the axis of said electrode surfaces for confiningA said material within the space between said electrodes; and both said reservoirs being also lilled with said material and being in communication with said chamber; whereby the range of pressure variation of said materialin said chamber is restricted and the modulation emciency of said microphone is maintained ata high level re gardless of its orientation.

'7. In a microphone, a vibratile diaphragm, two electrodes, `one of saidielectrodes being stationary and having a convex surface whichfis generally cone shaped and the other of saidelectrodes being movable with said diaphragm and having a concave surface which is generally truncated-l cone shaped, said two surfaces being coaxial with each other and with said diaphragm and facingI each other in mutually'spaced relation to deiinethe ends of a chamber; yieldableV closure means extending between and contiguously to the peripheral base portions of the cone formed by said surface of the stationary electrode and the truncated ccne formed by said surface of the Inov-4 able-electrode, generally cylindrically around said chamber to completelyfdene said chamber; com.- minuted resistance material completely filling said chamber and adapted to be compressed in accordance with incident sound waves; a first reservoir housing whichis disposed such that the end of said reservoir farthest away from said chamber is located above said chamber' when said microphone is oriented with said stationary electrode above said movable' electrode; and a second reservoirhousing which is formed by a recess in said movable electrode andr is disposed such that the end of said reservoir farthest away from said chamber islocated'above said chamber when said microphoneis oriented with said mov-A able electrode above said stationary electrode; said closure means being yieldable only in a direction substantially parallel to the axis of said electrode .surfaces forconning saidmaterial within the space between said electrodes; and both said reservoirs being also nlled with said material and being in. communication with said chamber; whereby the range of pressure variation of said material in said chamber is restricted and the modulation efficiency of said microphone is maintained at a high levelregardless of. its orientation.

8. In a microphone, a vibratile diaphragm, two electrodes, one of. said` electrodes bengstationary and having a convex surface which is generally cone shaped and the other of said. electrodes be.-

ing movable. with` said diaphragm and having ay concave surface which is generally truncatedcone shaped, said two surfaces being coaxial with each other andwith said diaphragm and facing each other in mutually spaced relation to define the ends of a chamber; yieldable closure means extending betweenI and contiguously to the peripheral base portions of the coneformed by said surface of the-stationary electrodeand the truncated cone formed by saidsurfaceof the'movable electrode, generally cylindrically around said chamber to completely define said chamber; comminuted resistance material completely filling said chamber and adapted to beY compressed in accordance with incident sound waves; a rst reservoir housing which is disposed such that the end of said reservoir farthest away from said chamber is located above said chamber when said microphone is oriented with said stationary electrode above said movable electrode; and a second reservoir housing which is disposed such that the end of said reservoir farthest away from said chamber is located above said chamber when said microphone is oriented with said movable electrode above said stationary electrode; said closure means being yieldable only in a direction substantially parallel to the axis of said electrode surfaces for conning said material Within the space between said electrodes; and both said reservoirs being also filled with said material and being in communication with said chamber; whereby the range of pressure variation of said material in said chamber is restricted and the modulation efciency of said microphone is maintained at a high level regardless of its orientation.

9. A microphone comprising a vibratile diaphragm, two electrodes, one of said electrodes being stationary and having a convex surface which is generally cone shaped and the other of said electrodes being movable with said diaphragm and having a concave surface which is generally truncated-cone shaped, said two surfaces being coaxial with each other and with said diaphragm and facing each other in mutually spaced relation to dene the ends of a chamber; yieldable closure means completely dening said chamber; comminuted resistance material completely filling said chamber and adapted to be compressed in l0 accordance with incident sound Waves; a rst reservoir housing which is located substantially in back of said stationary electrode as viewed from said movable electrode; and a second reservoir housing which is movable with said movable electrode, forms a recess extending centrally from the smaller end of said truncated cone away from said chamber, and is closed at its end farthest from said chamber; each of said electrodes having the acute angles between their respective generally cone shaped surfaces and their common axis smaller than the corresponding natural angle that would be assumed by said comminuted resistance material when heaped in an unconiined pile on a horizontal surface; and both said reservoirs being also lled with said material and being in communication with said chamber.

l0. A microphone as claimed in claim 9 characterized in that said rst reservoir opens into said chamber at the peripheral base portion of the cone formed by said surface of the stationary electrode and the second reservoir opens into said chamber centrally through the smaller end of the truncated cone formed by said surface of the movable electrode, whereby regardless of Whether the microphone is oriented With one or the other electrode uppermost, said chamber communicates with the then uppermost reservoir substantially at the then uppermost portion of said chamber.

WILLIAM ALFRED CODD.

REFERENCES CITED The following references are of record in the file of this pat-ent:

UNITED STATES PATENTS Number Name Date 2,191,992 McLarn Feb. 27, 1940 2,225,488 Stevens Dec. 17, 1940 

